1. Field of Invention
The present invention relates to an optical information recording medium on which information can be recorded and from which the information can be replayed by a laser, and a method for recording information. Specifically, the invention relates to a heat-mode optical information recording medium suitable for recording information with a laser having short wavelength of no more than 440 nm.
2. Description of the Related Art
Conventionally, an optical information recording medium (an optical disk) on which information can be recorded only once by a laser has been known. This optical disk is also referred to as a write-once CD (so-called a CD-R), and the typical constitution thereof comprises a transparent disc-shaped substrate, as well as a recording layer consisting of an organic dye, a light reflecting layer consisting of a metal such as gold and the like and a protective layer made of a resin, wherein these layers are provided onto the substrate in this order to form a laminate. The recording of information on the CD-R is carried out by irradiating a near-infrared laser (generally a laser having a wavelength of near 780 nm) on the CD-R, whereby the irradiated portion of the recording layer absorbs the beam, raises the temperature locally, which causes a physical or chemical change (for example, formation of a pit) to allow changing the optical properties of the portion. Thus, the information is recorded thereon.
In contrast to the above, reading (replaying) of the information on the CD-R is also carried out by irradiating a laser having the same wavelength as that for recording. The information is replayed by detecting the difference between the reflectance for the portion in which the optical properties of the recording layer has been changed (recorded portion) and that of the unchanged portion (unrecorded portion).
Recently, an optical information recording medium on which information can be recorded at high density has been required. In response to the request, an optical disk referred to as a write-once digital versatile disk (so-called a DVD-R) has been proposed (for example, “DVD”, that is a supplemental volume of “Nikkei New Media”, published in 1995). This DVD-R has a constitution in which two disks each comprising a transparent disc-shaped substrate on which a guide groove (a pr groove) for tracking the irradiated laser has been formed, which groove is half or less as narrow as that of a CD-R (0.74 to 0.8 μm), a recording layer comprising a dye provided onto the substrate, a light reflecting layer generally provided onto the recording layer, and optionally a protective layer, have been adhered by an adhesive, or a constitution in which the above-mentioned disk and a disc-shaped protective substrate having the same shape as that of the disk have been adhered by an adhesive, and in both constitution, the side in which the recording layer(s) have been provided is (are) facing inside. The recording and replaying of the information on the DVD-R is carried out by irradiating a visible laser (generally a laser having a wavelength of 630 nm to 680 nm), which is said to be capable of being recorded in higher density than that for the CD-R.
Recently, networks such as Internet and the like, a Hi-Vision TV, and the like have rapidly come into wide use. Furthermore, a HDTV (High Definition Television) will start to air in the near future. Thus, demands for a recording medium having large capacity for recording image information cheaply and easily have been increased. While a DVD-R keeps the post as a recording medium having large capacity to some extent, it does not necessarily have sufficiently large capacity that can deal with the future demands. Therefore, developments for an optical disk having even larger capacity are now proceeding, by using a laser having shorter wavelength than that for a DVD-R to allow improvement in recording density.
For example, Japanese Patent Application Laid-Open (JP-A) Nos. 4-74960, 7-304256, 7-304257, 8-127174, 11-53758, 11-334204, 11-334205, 11-334206, 11-334207, 2000-43423, 2000-108513, 2000-113504, 2000-149320, 2000-158818, 2000-228028, 2001-39034 and 2001-253171 disclose methods for recording and replaying information on an optical information recording medium having a recording layer comprising an organic dye, comprising irradiating a laser having a wavelength of 530 nm or less from the side of the recording layer to the side of a light reflecting layer. Specifically, the above-mentioned documents propose a method for recording and replaying information by irradiating an optical disk with a blue laser (wavelength: 430 nm or 488 nm) or a blue green laser (wavelength: 515 nm), which optical disk comprises a dye such as a porphyrin compound, an azo dye, a metallic azo dye, a quinophthalone dye, a trimethinecyanine dye, a dye having a dicyanovinylphenyl skelton, a coumarin compound, a naphthalocyanine compound, an oxazole compound and the like for a recording layer provided thereon.
According to the studies done by the present inventors, it has been found that the optical disks disclosed in the above-mentioned documents still require further improvements since they are still not sufficient in recording properties such as sensitivity during practical use, reflectance, modulation and the like.
Therefore, provision of an optical information recording medium, wherein information can be recorded and from which the information can be replayed by irradiating a laser having a shorter wavelength than those for a CD-R and a DVD-R, such as a laser having a wavelength of no more than 440 nm, specifically a highly-versatile semiconductor laser having a wavelength of near 405 nm (more specifically, in a range of 405 to 410 nm), and has superior recording properties (high sensitivity, high reflectance, high modulation), has been required.
Furthermore, provision of a method for recording information at high density by using an optical information recording medium comprising a recording layer comprising a dye compound that shows high sensitivity for a laser having short wavelength, has been specifically required.